Thermal switch

ABSTRACT

A two-piece plastic case having laterally spaced stationary contact pins extending transversely of the case interior and a movable contact comprising single strand of a spring conductor positioned within the case and tensioned transversely of its length to engage both pins. A detent having a relatively low melting temperature extends into the case through an opening in its wall and holds the moving contact out of engagement with one of the contact pins. Insulated external switch leads extend into the casing for electrical connection to the contact pins, respectively. A slot in the casing wall provides access to the movable contact from outside the casing for retracting or cocking it prior to insertion of the detent.

Charles F. Burney Milpitas, Calif.

Mar. 2, 1970 Aug. 31, 197i Inventor Appl. No. Filed Patented Assignee THERMAL SWITCH 4 Claims, 4 Drawing Figs.

U.S. Cl.

Int. Cl.

Sylvania Electric Products Inc.

H0111 37/76 Field of Search 402,407,4ll,4l3,414,416

References Cited UNITED STATES PATENTS 12/1953 Normand 4/ I 940 Lafleur ..L 2/1926 Kel1er et a1. 1/1916 Rattermann et a1. 6/ 1912 Emch Primary Examiner-Bemard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorneys-Norman J. OMalley, John F. Lawler and Russell A. Cannon ABSTRACT: A two-piece plastic case having laterally spaced stationary contact pins extending transversely of the case interior and a movable contact comprising single strand of a spring conductor positioned within the case and tensioned transversely of its length to engage both pins. A detent having a relatively low melting temperature extends into the case through an opening in its wall and holds the moving contact out of engagement with one of the contact pins. Insulated external switch leads extend into the casing for electrical connection to the contact pins, respectively. A slot in the casing wall provides access to the movable contact from outside the casing for retracting or cocking it prior to insertion of the detent.

PATENIEU M1831 um SHEET 1 BF. 2

INVENTOR.

CHARLES F. BURNEY ATTORNEY PATENTED AUG31 197:

SHEET 2 OF 2 'NVENTOR.

CHARLES F. BURNEY 44 ATTQRNEY THERMAL SWITCH BACKGROUND OF THE INVENTION The invention relates to electric switches and more particularly to anextremely low-cost temperature-sensitive electric switch.

Electric switches which close automatically in response to heat generally are constructed to be resettable to the initial or normal position. This enables the switch to be used again once it has been tripped and permits testing of circuits associated with the switch. Examples of such resettable switches are a circuit breaker with a manual reset mechanism and the bimetallic switch which resets automatically. Such types of switches, however, are inherently relatively costly to produce and are therefore not economically suitable as heat sensors for home fire detection apparatus because of price sensitivity of the homeowner for such safety systems.

'An object of this invention is the provision of a reliable heat responsive switch of extremely simple low-cost construction.

SUMMARY OF THE INVENTION contact and thus closes the switch.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a switch assembly embodying the invention, the cover of the switch casing being broken away to show details of construction;

FIG. 2 is a section taken on line 2-2 of FIG. 1; and FIGS. 3 and 4 are views similar to FIG. 1 showing modified forms of the invention.

" DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, a switch 5 embodying the invention is shown in FIGS. 1 and 2 connected to lines L, and L forcontrolling energization of an external circuit coupled to these lines and consisting of a source B of electrical energy, such as a battery, and utilization apparatus C such as a bell. Switch 5 comprises a casing composed of electrically nonconductive material such as plastic and having a base wall 11 and integral sidewalls 12, 1'3, 14 and 15, and a preferably metallic cover 16 removably secured by screws 17 to the casing sidewalls. Ca sing l0 also has an integral intermediate wall 18 which abuts the underside of cover 16 and together with the adjacent sidewalls defines a compartment 19 for retaining 'a knotted portion of lines L, and L adjacent to casing wall opening 20 through which the lines extend. Ends 18a and 18b of wall" 18 are spaced from sidewalls l2 and 14, respectively,

to permit lines L, and L to extend into switch compartment 2l on the opposite side of theintermediate wall.

The stationary switch contacts are substantially-identical laterally spaced parallel pins 23 and 24 which are secured to and extend through base wall 11 into compartment 21 for a distance slightly less than the depth of the latter so as to be spaced from cover 16. Pins 23' and 24 preferably are configured with spaced' shoulders as shown and each is permanently electrically connected adjacent to base wall 11 to a terminal 25 on the end of the associated line L, or L Moving contact 27 of this switch consists of a single conductive strand of spring wire configured in a U-shape similar to a safety pin with two legs 27a and 27b projecting from a coil portion 270. A fixedpost 29 preferably integral with base wall l l projects therefrom across compartment 21 generally parall'el with and offset from pins 23 and 24 and'anchors the coiled strand portion 270 which is wound thereabout. Legs 27a and 27b extend between and' overlie pins 23 and 24 and are tensioned by 'coil 27c to-normally move apart toward and into engagement with the pins; leg 27b operatively engages contact pin 24 continuously. I

In accordance with the invention, a detent 30 is disposed between stationary contact 23 and movable contact leg 27a to hold the switch open. Detent 30 has a cylindrical stem 300 which extends snugly through opening 31 in cover 16 into the path of movement of leg 27a and an enlarged head 30!; which abuts the exterior or the cover when the detent is fully inserted. The material of which detent 30 is composed is sufficiently rigid when cool, i.e., at room temperatures, to hold leg 27a in its tensioned or cocked" positionas shown in solid lines in FIG. 1 and yet is responsive to heat to soften or melt at a temperature well below the melting temperature of the other parts of the assembly so as to unblock leg 27a and permit it to snap into engagement with pin 23 as shown in broken lines to close the switch when such a heat condition prevails. By way of example, detent 30 may be made of an alloy of Wood's metal and lead having a melting temperature of 147 F.- and marketed under the trademark Cerrolow by United Refining and Smeltirig Company of Chicago, Illinois. Cover 16 has high thermal conductivity to facilitate transmission of ambient heat to the detent and for this purpose may be aluminum or an aluininum alloy. Line L may be grounded as indicated at G so that contact pin 24 to which it is connected along with detent 30 and cover 16 are not electrically hot.

In order to check the operation of the switch when making a system test, detent30 simply is physically removed from the casing, thus disengaging contact arm 270 which snaps into engagement with pin 23 to close the switch. In order to permit resetting of the switch, a slot 32 is formed in base wall 11 aligned with and extending on opposite sides of detent stem 30a. A small tool such as a screwdriver may be inserted through slot 32 to retract arrn27a prior to reinsertion of detent 30 in the operative position. As shown, the width of slot 32 is less than the diameter of detent 30a and recess 33 on the inside of base wall 11 in alignment with cover opening 31 provides a seat for the detent. v t

It will be noted that casing 10 and cover 16 provide an effective protective enclosure which may readily be mounted in strategic locations to detect conditions which generate exces- V plifying construction and minimizing the number of parts required for the assembly. The action of detent 30 in positively blocking movement of contact arms 27a in the absence of excessive heat insures against inadvertent tripping of the switch even when accidentally jolted or struck.

An alternate embodiment of the invention is shown in FIG. 3 in which the spring wire movable contact 37 is L-shaped and has a tensioned long leg 37a held out of engagement with one stationary contact 23' by a similar detent 30' and a similarly tensioned short leg 37b hooked over and anchored on the other stationary contact 24'. Thus strand 37 is not coiled around post 29' but is simply bent substantially at a right angle about this post so as to cause leg 37a to exert a torque against the detent.

Another embodiment of the invention is shown in FIG. 4

wherein the spring wire contact 47 in the cocked position is concavo-convexly bowed around detent 30" in the manner of a toggle with the concave side engaging the detent and opposite ends of the convex side engaging casing sidewall 14" and stationary contact pin 24", respectively. When detent 30" melts or is otherwise removed from the switch casing, contact 47 tends to straighten and snaps into engagement with stationary contact 23" to close the switch. In other respects,

the switch assemblies shown in FIGS. 3 and 4 are substantially the same as that shown in FIG. 1 and like parts are indicated by the primes of like reference characters.

I claim:

1. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls and an integral post a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions ofsaid lines, said cover having an opening therein,

a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure,

said pins being electrically connected to said lines, respectively,

said integral post being between and offset from said pins,

an electrically conductive U-shaped spring element having a coiled part wound about said post and having one portion thereof extending from said coiled part electrically connected to one of said pins and another portion thereof extending from said coiled part movable between a first position spaced from the other pin and a second position in engagement with said other pin,

said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position,

a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter i said first position,

said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.

'2. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls and an integral post,

a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein,

a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior ofsaid enclosure,

said pins being electrically connected to said lines, respectively,

said integral post being between and offset from said pins,

an electrically conductive L-shaped spring element bent partially around said post and having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin,

said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position,

a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position,

said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.

3. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls, a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein,

a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure,

said pins being electrically connected to said lines, respectively,

an electrically conductive spring element having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin,

said element being self-tensioned in a concave-convex shape and being disposed with opposite ends of the convex side engaging a sidewall of the casing and said one of said pins, respectively, for producing movement of said another portion in a direction from said first position to said second position,

a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position,

said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.

4. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls, said base wall having a slot therein,

a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein,

a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure,

said pins being electrically connected to said lines, respectively,

an electrically conductive spring element having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin,

said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position,

said base wall slot being aligned with the direction of movement of said one portion of the element between said first and second positions whereby to permit access to the interior of the casing from the exterior for resetting said element,

a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position,

said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position. 

1. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls and an integral post a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein, a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure, said pins being electrically connected to said lines, respectively, said integral post being between and offset from said pins, an electrically conductive U-shaped spring element having a coiled part wound about said post and having one portion thereof extending from said coiled part electrically connected to one of said pins and another portion thereof extending from said coiled part movable between a first position spaced from the other pin and a second position in engagement with said other pin, said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position, a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position, said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.
 2. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls and an integral post, a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein, a pair of laterally spaced parallel electrically conductive pins secured to said baSe wall and extending transversely of the interior of said enclosure, said pins being electrically connected to said lines, respectively, said integral post being between and offset from said pins, an electrically conductive L-shaped spring element bent partially around said post and having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin, said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position, a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position, said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.
 3. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls, a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein, a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure, said pins being electrically connected to said lines, respectively, an electrically conductive spring element having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin, said element being self-tensioned in a concavo-convex shape and being disposed with opposite ends of the convex side engaging a sidewall of the casing and said one of said pins, respectively, for producing movement of said another portion in a direction from said first position to said second position, a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position, said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position.
 4. A switch for a pair of electrical lines comprising an electrically nonconductive casing having a base wall and integral sidewalls, said base wall having a slot therein, a cover secured to said sidewalls spaced oppositely from said base wall and defining with said casing an enclosure for the two end portions of said lines, said cover having an opening therein, a pair of laterally spaced parallel electrically conductive pins secured to said base wall and extending transversely of the interior of said enclosure, said pins being electrically connected to said lines, respectively, an electrically conductive spring element having one portion thereof electrically connected to one of said pins and another portion thereof movable between a first position spaced from the other pin and a second position in engagement with said other pin, said element being self-tensioned for producing movement of said another portion in a direction from said first position to said second position, said base wall slot being aligned with the direction of movement of said one portion of the element between said first and second positions whereby to permit access to the interior of the casing from the exterior for resetting said element, a detent projecting from outside the enclosure through said opening in said cover into the path of movement of said another portion of said element for holding the latter in said first position, said detent being sufficiently rigid at room temperatures to hold said another portion of said element in said first position and being responsive to heat at elevated temperatures less than the melting temperature of said casing to soften and unblock movement of said another portion of the element to said second position. 